61A Lecture 12
Announcements
Objects
(Demo)
Objects
4
Objects
•Objects represent information
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs•Special syntax that can improve the composition of programs
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs•Special syntax that can improve the composition of programs
• In Python, every value is an object
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs•Special syntax that can improve the composition of programs
• In Python, every value is an object
• All objects have attributes
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs•Special syntax that can improve the composition of programs
• In Python, every value is an object
• All objects have attributes• A lot of data manipulation happens through object methods
4
Objects
•Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes
• A type of object is called a class; classes are first-class values in Python
• Object-oriented programming:
•A metaphor for organizing large programs•Special syntax that can improve the composition of programs
• In Python, every value is an object
• All objects have attributes• A lot of data manipulation happens through object methods• Functions do one thing; objects do many related things
4
Example: Strings
(Demo)
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
• Rows indexed 2-5 are a useful 6-bit (64 element) subset
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
• Rows indexed 2-5 are a useful 6-bit (64 element) subset
• Control characters were designed for transmission
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
• Rows indexed 2-5 are a useful 6-bit (64 element) subset
• Control characters were designed for transmission
"Line feed" (\n)
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
• Rows indexed 2-5 are a useful 6-bit (64 element) subset
• Control characters were designed for transmission
"Line feed" (\n)"Bell" (\a)
6
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange8
rows
: 3
bits
16 columns: 4 bits
• Layout was chosen to support sorting by character code
• Rows indexed 2-5 are a useful 6-bit (64 element) subset
• Control characters were designed for transmission
"Line feed" (\n)"Bell" (\a)
6
(Demo)
Representing Strings: the Unicode Standard
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
U+263a WHITE SMILING FACE
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
U+263a WHITE SMILING FACE
U+2639 WHITE FROWNING FACE
7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
U+263a WHITE SMILING FACE
U+2639 WHITE FROWNING FACE
'☺'7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
U+263a WHITE SMILING FACE
U+2639 WHITE FROWNING FACE
'☺' '☹'7
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
•109,000 characters•93 scripts (organized)•Enumeration of character properties, such as case
•Supports bidirectional display order•A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
U+263a WHITE SMILING FACE
U+2639 WHITE FROWNING FACE
'☺' '☹'7
(Demo)
Mutation Operations
Some Objects Can Change
9
[Demo]
Some Objects Can Change
First example in the course of an object changing state
9
[Demo]
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👶same_person
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👶BABY
same_person
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👶BABY
same_person
Unicode character
name
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👧GIRL
same_person
Unicode character
name
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👧GIRL
jessicasame_person
Unicode character
name
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👩WOMAN
jessicasame_person
Unicode character
name
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👵OLDERWOMAN
jessicasame_person
Unicode character
name
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👵OLDERWOMAN
jessicasame_person
Unicode character
name
All names that refer to the same object are affected by a mutation
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👵OLDERWOMAN
jessicasame_person
Unicode character
name
All names that refer to the same object are affected by a mutation
Only objects of mutable types can change: lists & dictionaries
Some Objects Can Change
First example in the course of an object changing state
The same object can change in value throughout the course of computation
9
[Demo]
👵OLDERWOMAN
jessicasame_person
Unicode character
name
All names that refer to the same object are affected by a mutation
Only objects of mutable types can change: lists & dictionaries
{Demo}
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
def mystery(s): s.pop() s.pop()
Interactive Diagram
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
def mystery(s): s.pop() s.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
>>> four = [1, 2, 3, 4]
def mystery(s): s.pop() s.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
>>> four = [1, 2, 3, 4]>>> len(four)4
def mystery(s): s.pop() s.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
>>> four = [1, 2, 3, 4]>>> len(four)4>>> another_mystery() # No arguments!
def mystery(s): s.pop() s.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
>>> four = [1, 2, 3, 4]>>> len(four)4>>> another_mystery() # No arguments!>>> len(four)2
def mystery(s): s.pop() s.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]>>> len(four)4>>> mystery(four)>>> len(four)2
>>> four = [1, 2, 3, 4]>>> len(four)4>>> another_mystery() # No arguments!>>> len(four)2
def mystery(s): s.pop() s.pop()
def another_mystery(): four.pop() four.pop()
Interactive Diagram
def mystery(s): s[2:] = []
or
Tuples
(Demo)
Tuples are Immutable Sequences
12
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
Name change:
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change:
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change:
>>> x = 2
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change:
>>> x = 2
4
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change:
>>> x = 2
4>>> x = 3
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change:
>>> x = 2
4>>> x = 3
6
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4ERROR
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4ERROR
>>> s = ([1, 2], 3)
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4ERROR
>>> s = ([1, 2], 3)>>> s[0][0] = 4
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4ERROR
>>> s = ([1, 2], 3)>>> s[0][0] = 4>>> s
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects
An immutable sequence may still change if it contains a mutable value as an element
>>> turtle = (1, 2, 3)>>> ooze()>>> turtle(1, 2, 3)
>>> turtle = [1, 2, 3]>>> ooze()>>> turtle['Anything could be inside!']
>>> x + x
>>> x + x
Name change: Object mutation:
>>> x = 2
4>>> x = 3
6
>>> x = [1, 2]
[1, 2, 1, 2]>>> x.append(3)
[1, 2, 3, 1, 2, 3]
>>> s = ([1, 2], 3)>>> s[0] = 4ERROR
>>> s = ([1, 2], 3)>>> s[0][0] = 4>>> s([4, 2], 3)
>>> x + x
>>> x + x
Next lecture: ooze can change turtle's binding
Mutation
Sameness and Change
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a>>> a == bTrue
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
14
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]>>> a == bTrue
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]>>> a == bTrue>>> b.append(20)
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]>>> a == bTrue>>> b.append(20)>>> a[10]
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]>>> a == bTrue>>> b.append(20)>>> a[10]>>> b[10, 20]
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Sameness and Change
• As long as we never modify objects, a compound object is just the totality of its pieces
• A rational number is just its numerator and denominator
• This view is no longer valid in the presence of change
• A compound data object has an "identity" in addition to the pieces of which it is composed
• A list is still "the same" list even if we change its contents
• Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10]>>> b = [10]>>> a == bTrue>>> b.append(20)>>> a[10]>>> b[10, 20]>>> a == bFalse
>>> a = [10]>>> b = a>>> a == bTrue>>> a.append(20)>>> a == bTrue>>> a[10, 20]>>> b[10, 20]
Identity Operators
15
Identity Operators
Identity
<exp0> is <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to the same object
15
Identity Operators
Identity
<exp0> is <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to the same object
Equality
<exp0> == <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to equal values
15
Identity Operators
Identity
<exp0> is <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to the same object
Equality
<exp0> == <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to equal values
Identical objects are always equal values
15
Identity Operators
Identity
<exp0> is <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to the same object
Equality
<exp0> == <exp1>
evaluates to True if both <exp0> and <exp1> evaluate to equal values
Identical objects are always equal values
15
(Demo)
Mutable Default Arguments are Dangerous
16
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]):... s.append(3)... return len(s)...
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]):... s.append(3)... return len(s)... >>> f()1
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]):... s.append(3)... return len(s)... >>> f()1>>> f()2
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]):... s.append(3)... return len(s)... >>> f()1>>> f()2>>> f()3
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16Interactive Diagram
>>> def f(s=[]):... s.append(3)... return len(s)... >>> f()1>>> f()2>>> f()3
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16Interactive Diagram
>>> def f(s=[]):... s.append(3)... return len(s)... >>> f()1>>> f()2>>> f()3
Each time the function is called, s is bound to the same value!